Add Playwright for end-to-end tests

[dunkOnIT]

Info

It does seem like playwright and @playwright/test were conflicting - I removed them both in my local, and reinstalled just @playwright.test. I believe this is the correct approach, as Playwright Test includes the Playwright Library, per their documentation:

Playwright Library provides unified APIs for launching and interacting with browsers, while Playwright Test provides all this plus a fully managed end-to-end Test Runner and experience. [emphasis mine]

I've confirmed that comp PDF generation still works locally even with these changes.

Todo

• [x] Basic setup with Playwright's example tests
• [x] Assess diff / contents of playwright setup
• [x] Ensure that existing playwright dependencies still work
• [x] Write an actually meaningful E2E test
• [x] Get that test to execute in the CI

[dunkOnIT]

I've updated the PR such that it works in local when I run yarn playwright test. This is enough for now to start getting a frontend test framework going - once we have some kind of skeleton going there which is worth running in CI, I'll add the system-tests workflow again. For now, I've got it on its own branch in my repo